This invention relates to forming electrical interconnection between an integrated circuit chip and a substrate. In particular, the invention relates to interconnecting an integrated circuit chip with the substrate in a flip chip semiconductor device package.
Interconnection between an integrated circuit chip and a substrate such as a printed circuit substrate is commonly formed during assembly of the device package. In a commonly used interconnection method, gold bumps are mounted on the integrated circuit chip in an arrangement corresponding to the arrangement of metal contact pads on the substrate. During package assembly the chip and the substrate are apposed with the corresponding bumps and pads aligned; then the chip and substrate are brought together under conditions (temperature, pressure, untrasonic vibration) that promote bonding of the bumps onto the metal pads.
The surfaces of the integrated circuit chip and the substrate are not uniformly flat. The substrate, which may be formed of an organic polymer, may have a particularly nonflat surface, particularly where the substrate is fabricated using a lower cost process. The substrate surface may be warped or may otherwise have irregularities. Accordingly, the surfaces of the metal contact pads on the substrate may be noncoplanar. As a result, when the surfaces of the chip and the substrate are apposed, the various metal pad surfaces are at different distances from the corresponding contact surfaces of the chip. Because of this irregularity, when the chip and the substrate are brought together, some of the bumps may fail to make good contact with their corresponding pads, resulting in a nonfunctioning package.
There is a continual demand in industry for reduced size in semiconductor packages. As packages are made smaller, the interconnect structures are also made smaller and the clearance between the chip and the substrate becomes narrower. Where the clearance between the chip and the substrate is very narrow even comparatively slight noncoplanarities of the substrate surface become significant, and can result in an unacceptable rate of interconnect failure during package construction.
There is a need for improved reliability in construction of robust interconnects in electronic chip package assembly.